Here is good argument against using pressure on a roof. This is a pic of a portion of the roof that was pressured washing using a pitch witch. He did not use any chemical or cleaner. Just straight water and pressure. The only part he washed the upper right portion of the roof. As you can see that portion is now lighter due to granule loss. The granules not only have reflective properties, but aesthetic purposes also. Granule loss will make the roof look lighter and non-uniform such as in this pic. Darker roofs have a more dramatic effect as you can see. This is a good bit of info you can tell your potential customers.
Please feel free to use this pic on your website if you'd like or just as a reference for you. I will take another pic when the sun is out to see if the effect is more dramatic and if so I will post it on here. thanks
-- Edited by mlacey1977 on Thursday 15th of October 2009 01:37:00 PM
Mike can you email me a copy of that picture to me and I would like to add it to my portfolio to show people, that is a good idea for picture. It wasn't a customer though was it? Good reference point.